Field of the Invention
The present invention relates to the field of part molding.
More particularly, the invention relates to a mold comprising a first shell and a second shell that are suitable, in the closed position, for imparting a shape to a part that is to be molded in the mold, a main axis A being perpendicular to the main plane in which the first shell and the second shell extend.
Description of the Related Art
A mold used for molding a part comprises a first shell and a second shell. Each shell possesses a shape that is more or less complex depending on the shape desired for the part after it has been molded, nevertheless, each shell extends essentially in a main plane. The main axis is defined as being the axis that is perpendicular to the main plane of the first shell, and to the main plane of the second shell when the mold is in the closed position.
The mold is in the closed position when the first shell and the second shell are in contact with each other around all (or practically all) of their periphery so as to imprison a volume that is to be filled with the material of the part during the process of molding the part.
The molded part may for example be made of a polymer, or of a composite material constituted by a polymer reinforced by fibers (e.g. carbon fibers).
The molding method comprises a stage of heating the part to a temperature higher than ambient temperature, during which the first shell and the second shell are held pressed one against the other (closed position). When the molded part is made of polymer, this heating stage comprises a stage of polymerizing the polymer, at a temperature lying in the range 80° C. to 500° C. The mold is in a closed position not only during this heating stage, but also during subsequent cooling of the molded part down to its unmolding temperature, so as to ensure that the part takes on the desired shape (the shape defined by the volume between the two shells). When the molded part is made of a polymer or of a composite, this unmolding temperature is lower than the glass transition temperature of the polymer. By way of example, this unmolding temperature may be ambient temperature.
Such molds present drawbacks. Specifically, the material of the molded part usually presents a coefficient of thermal expansion that is different from the coefficient of thermal expansion of the material constituting the first shell and the second shell. When the coefficient of expansion of the part is less than that of the shells in at least one direction, then this difference leads to undesirable stresses being applied to the part while it is cooling, which stresses run the risk of irreversibly damaging the part and/or can lead to difficulties in extracting the part from the mold since the part remains jammed tightly in the mold.